鄂尔多斯盆地吴起—安塞地区长81亚段砂岩储层致密成因及其对油气藏分布的影响

Causes of Chang 81 sandstone reservoir densification in Wuqi-Ansai area,Ordos Basin and its influence on reservoir distribution

鄂尔多斯盆地吴起—安塞地区上三叠统长81亚段尚未实现规模开发,储层致密是其主要原因之一。为明确长81亚段储层致密的原因,基于沉积学、岩石学、储层成岩作用及孔隙演化等理论,分析野外露头、钻井、测井及岩心分析试验等资料,并将研究区与陇东、姬塬地区进行对比以探讨长81亚段储层致密的成因。结果表明:吴起—安塞地区长81亚段砂岩碎屑颗粒搬运距离远、粒度小,塑性组分含量高;分流河道及水下分流河道微相沉积形成一套细粒砂岩储层;压实作用、伊利石黏土矿物和碳酸盐胶结作用使砂岩整体变致密;微观孔隙结构整体表现为小孔隙、微喉道,大于10μm的微米级孔隙构成了油气储集的主要空间。研究认为,远源三角洲形成的细粒沉积、强烈的黏土矿物和碳酸盐胶结作用是造成吴起—安塞地区长81亚段储层致密的主要原因。这一认识对指导研究区及类似地区致密砂岩油气勘探具有重要意义。

The Upper Triassic Chang 81 sub-member in Wuqi-Ansai area,Ordos Basin has not been developed on a large scale.Tight reservoir is one of the main reasons based on sedimentology,petrology,reservoir diagen⁃esis and pore evolution.This paper analyzes the data of outcrop,drilling,logging and core analysis,and com⁃pares the study area with Longdong and Jiyuan areas to explore the causes of Chang 81 sub-member tight reser⁃voir.The results show that:the transport distance of clastic particles of Chang 81 sub-member sandstone in WuqiAnsai area is long,the particle size is small,and the content of plastic components is high.The distributary channel and underwater distributary channel microfacies formed a set of fine grained sandstone deposit.Compac⁃tion,illite clay minerals and carbonate cementation densified the sandstone as a whole.The micropore structure as a whole shows small pores and micro throats.Micrometer pores larger than 10µm constitute the main space of oil and gas storage.Studies suggest that the fine-grained deposits formed in the far-source delta,strong clay minerals and carbonate cementation are the main reasons for the tight reservoir of Chang 81 sub-member in Wuqi-Ansai area.This understanding is of great significance to guide the exploration of tight sandstone oil and gas in the study area and similar areas.